GLOSSARY OF TERMS USED ON THE CHARTS AND IN THE MANUAL 303 



Pellicle, bacterial growth forming either a continuous or an interrupted 



sheet over the culture fluid ; a thick membrane. 

 Peptonization, conversion of (milk) protein into peptone by the action 



of proteolytic enzymes. 

 Peritrichic, having flagella distributed over the whole surface. 

 Per OS, through the mouth. 

 Persistent, lasting, in contrast to transient. 

 Phase, a recognizable stage in the growth of bacteria. 

 Phase variation, separation of a species into strains having somewhat 



different characters. (See Dissociation.) 

 Photic characters, characteristics relating to light. 

 Photogenic, glowing in the dark, phosphorescent. 

 Physiology, study of the functioning of organisms. 

 Polar, at the end or pole of the bacterial cell. 



Precipitin, an antibody which causes the precipitation of soluble antigens. 

 Pulvinate, cushion-shaped. 

 Punctiform, point-shaped, i.e., very small, but visible to naked eye; under 



1 mm in diameter. 

 Radiate, to diverge or spread from a common point. 

 Radiately ridged, ridges extending out from a center. 

 Raised, groAvth thick, with abrupt or terraced edges. 

 Reaction, as used here, refers to the hydrogen-ion concentration, i.e., 



pH of a solution. 

 Reduction, basically, the gain of electrons by a substance. May be 



accomplished by removal of oxygen from or the addition of hydrogen 



to the substance. A corresponding oxidation always accompanies 



reduction. Reduction refers here specifically to the conversion of 



nitrate to nitrite, ammonia or free nitrogen, also to the decolorization 



of litmus and other indicators. 

 Reduction of indicators, reduction of certain colored compounds by 



bacteria, resulting in loss of color. 

 Rennet curd, coagulation of protein of milk due to rennet or rennetlike 



enzymes; distinguished from acid curd by the absence of acid. 

 Rhizoid, growth of an irregular branched or rootlike character, as colonies 



of Bacillus mycoides. 

 Ring, growth at the surface of a liquid culture, often adhering to the glass. 

 Rod, a bacterial cell having a straight central axis which is longer than the 



diameter of the cross section of the cell. 

 Rough, colonies with an irregular, nonsmooth surface. 

 Rounded, circular or semicircular. 

 Rugose, wrinkled. 



Saccate, hquefaction in form of an elongated sac; tubular, cylindrical. 

 Saprophytic, living on dead organic matter. 



